Many small articles, such as beverages, beverage containers, food, small machine parts and other small items, are packaged in pallet load lots. Pallet loads are large stacks of articles or boxes of articles which are held on a flat support or pallet. The pallets may carry bulk items, such as beverage cans, or boxes or cases, each of which contain several items. The pallet and the goods on it can be moved as a unit from manufacture and packaging through distribution and ultimate use of the goods. Pallets are often moved in the distribution system by fork lift trucks which transport the entire pallet from place to place, or by conveyors.
A variety of machines have been devised to load and unload palletized materials, since manual handling is slow and expensive. These devices are known as palletizers or depalletizers by the industry. A typical palletizing machine is described and disclosed in U.S. Pat. No. 3,056,513. Stacking and unstacking devices are also described in U.S. Pat. Nos. 1,095,319; 1,365,120; 2,005,906; 2,257,469; 2,315,003; 2,634,852; 2,699,264; 2,701,650; 2,857,040; 2,875,907; and 2,901,128. The disclosures of all of the above patents are incorporated by reference herein.
The state of the art palletizing and depalletizing machines use a bottom ejecting technique which requires that a pallet be returned to the bottom of the machine and ejected when empty. This introduces a period of dead time into the machine during which no loading or unloading is taking place and slows down the total throughput of the machine. As a result, in many operations, it is necessary to provide some mens to accumulate material in the system so that the other operations in the total system can be continued during the times that the loading or unloading device is cycling pallets in or out of the machine.
For example, in high speed beverage canning operations, bulk cans are unloaded by a depalletizer having a bottom ejecting operation. In order to supply sufficient cans to the canning operation, a long accumulating conveyor is required which has enough lag in it that cans can be continuously fed to the canning machine. These conveyors are quite long, occupy a great deal of expensive space, which could be used for other purposes in the plant, and are expensive to purchase and maintain.
Accumulating conveyors are also required in palletizing operations which have bottom feeding of empty pallets, since time is required to cycle an unloaded pallet up to the ready position after ejection of the loaded pallet. The conveyors provide a lag to hold the flow of materials which is interrupted by the cyclic ejection of a loaded pallet.
Applicant has devised a unique top ejecting and top feeding palletizing and depalletizing machine which can produce considerable savings in the time required to eject unloaded pallets from the machine, in feeding pallets to be loaded into the machine and in the time required to sequence subsequent pallets into the machine for loading and unloading. This device can be used to supply materials, for example cans to a high speed bottling operation, without the necessity for extensive accumulating conveyors since the gaps in the flow of cans, or other materials, are much smaller than the current state of the art devices. This enables the depalletizing machine to be placed much closer to the equipment which will use materials fom the depalletizing machine and saves not only in conveyors, conveyor maintenance cost and in space. The palletizing machine made can be operated much closer to the output machine without the necessity of extensive accumulating conveyors and other anciliary handling devices and in a savings in space due to the greater throughput.
Other and further advantages are apparent from the detailed description of the preferred embodiments which follows and from the drawings.